1. Field of the Invention
The present invention relates to a pixel structure and a driving method thereof, and more particularly, to a pixel structure used to minimize color washout effect and a driving method thereof.
2. Description of the Prior Art
An advanced monitor with multiple functions is an important feature for use in current consumer electronic products. Liquid crystal displays (LCDs) which are colorful monitors with high resolution are widely used in various electronic products such as monitors for mobile phones, personal digital assistants (PDAs), digital cameras, laptop computers, and notebook computers.
Thin-film-transistor liquid crystal displays (TFT-LCDs) have gradually become mainstream products in the consumer electronics market, for they have many merits such as high picture quality, efficient utilization of space, low consumption power, no radiation, etc. Referring to FIG. 1 showing an equivalent circuit diagram of a pixel unit 100 on a conventional LCD panel, the pixel units 100 on the LCD panel corresponds to a scan line G(m), a data line D(n), and a common line C(m). Also, the unit 100 comprises a thin film transistor (TFT) T, a liquid crystal (LC) capacitor CLC, and a storage capacitor CST. The TFT T controls conduction and disconnection according to a scan signal through the scan line G(m). When the scan signal is at a high voltage level, the TFT T turns on, causing data voltage applied on the data line D(n) to be delivered to the LC capacitor CLC and to the storage capacitor CST, so that the LC capacitor CLC and the storage capacitor CST are charged.
Referring to FIG. 2, FIG. 2 illustrates a waveform diagram of a scan signal applied on the pixel unit 100 shown in FIG. 1. The LCD panel comprises a plurality of pixel units 100, and each of the plurality of pixel units 100 corresponds to one of the scan lines G(m−1)˜G(m+1) and to one of the data lines D(n−1)˜D(n+1), respectively, as FIG. 2 shows. For brevity, the common line connected to each of the plurality of pixel units 100 is omitted in FIG. 2. Scan signals transmitted through each of the scan lines G(m−1)˜G(m+1) are generated sequentially. In other words, the scan signals are sequentially input to the neighboring scan lines G(m−1)˜G(m+1), so that the scan signals applied on the neighboring scan lines G(m−1)˜G(m+1) sequentially correspond to the high voltage level, causing the TFT T in the pixel unit 100 to conduct. Data voltage is stored in the storage capacitor CST and in the LC capacitor CLC corresponding to the pixel unit 100 row by row through the data lines D(n−1)˜D(n+1) and thereby a desired gray level is shown.
Currently, LCDs with a high contrast ratio, a swift response time, and a wide viewing angle are designed in accordance with the needs of the market. LCDs with a wide viewing angle can be designed with the technology like multi-domain vertically alignment (MVA), multi-domain horizontal alignment (MHA), twisted nematic plus wide viewing film (TN+film), and in-plane switching (IPS). Although the MVA technology can be implemented on TFT-LCDs to make the TFT-LCDs with a wide viewing angle, a problem of color washout occurs, which is blamed by the public. The color washout is that an image displayed on a LCD panel shows different colors in different sights of viewing angles. For instance, a user may see an image with a whiter color when his/her sight is at a more slanted angle with respect to the LCD panel.
Referring to FIG. 3, FIG. 3 is an equivalent circuit diagram showing a pixel unit 400 having a function of compensation for color washout according to conventional technology. The pixel unit 400 corresponds to two scan lines G1(m) and G2(m), a common line C(m), and a data line D(n). Further, the pixel unit 400 is divided into two pixel parts 400a and 400b. Each of the pixel parts 400a and 400b basically comprises the pixel unit 100 shown in FIG. 1. To be more specific, the pixel part 400a comprises a transistor S1, an LC capacitor CLC1, and a storage capacitor CST1. The pixel part 400b comprises a transistor S2, an LC capacitor CLC2, and a storage capacitor CST2. The pixel part 400a and the pixel part 400b correspond to the scan line G1(m) and the scan line G2(m), respectively.
Referring to FIG. 4, FIG. 4 illustrates waveforms of the scan signal applied on the pixel units 400a and 400b shown in FIG. 3. The LCD panel comprises a plurality of pixel units 400. For brevity, the common line C(m) is omitted in FIG. 4. Each of the plurality of pixel units 400 comprises two pixel parts 400a and 400b, as shown in FIG. 4.
The driving method of driving the pixel unit 400 is similar to that of driving the pixel unit 100. Scan signals are sequentially input to the neighboring scan lines G1(m)˜G2(m+1), so that the neighboring scan lines G1(m)˜G2(m+1) sequentially correspond to a high voltage level in an order of G1(m)→G2(m)→G1(m+1)→G2(m+1), causing the TFTs in the pixel unit 400 to conduct. Data voltage is stored in the storage capacitors CST1 and CST2 and in the LC capacitors CLC1 and CLC2 corresponding to the pixel unit 400 column by column through the data lines D(n−1)˜D(n+1) and thereby a correct frame is shown. Obviously, the method has a problem of doubling the number of the scan lines, causing the valid charging duration to be reduced to half the original one. Thus, such kind of technology is unable to be implemented in an LCD having a higher frame rate due to insufficient charging duration.
In addition, the received digital image data carried by data voltage transmitted through the data lines D(n−1)˜D(n+1) has to be transformed into analog data voltage by using a gamma circuit. Practically, the analog data voltage corresponds to different gray levels. When the pixel unit 400 receives scan signals, the pixel unit 400 drives LC molecules to display different gray levels in accordance with the analog data voltage transmitted through the data line. Since each of the plurality of pixel units 400 comprises two pixel parts 400a and 400b and gray levels of the two pixel parts 400a and 400b are required to be different in this technology, color washout can be solved even though a user sees on the LCD panel at different viewing angles. The reason why color washout can be solved is that the two different gray levels are complementary. However, the digital image data is input to two gamma circuits at the same time, and then the pixel parts 400a and 400b respectively receive different kinds of analog data voltage to increase flexibility of color correction in this pixel structure. An overall manufacturing cost of the circuit is increased due two gamma circuits used. Therefore, there is a need for a new pixel driving structure for solving the problem mentioned above.